KEY. J. F. BLAKE ON THE PORTLHSTD ROCKS OF ENGLAND. 189 



14. On the Portland Kocks of England. By the Eev. J. F. Blake, 

 M.A., F.G.S. (Bead January 7, 1880.) 



[Plates VIII.-X.] 



Unlike the Kimmeridgian and Corallian rocks, the Portland 

 series has been frequently examined in all its localities by compe- 

 tent observers, and there might seem, at first sight, to be little ad- 

 ditional or desirable information to obtain. Yet when all the 

 extant materials are put together they seem to serve but slightly 

 towards the history of the deposits in their varying relations to each 

 other and to similar rocks abroad. There is first the masterly work 

 of Pitton, forming the basis of our present knowledge ; yet many ques- 

 tions have arisen since its epoch which wait for a reply. The typical 

 sections along the coast have been touched on by several authors — as 

 Buckland and De la Beche *, Bristowf, and Damon ±; and the Port- 

 land stone has been well described ; but the lower part of the series has 

 been neglected. The district of the Yale of Wardour has attracted little 

 attention, though it has been mapped by the officers of the Geological 

 Survey. Of the important exposures in the neighbourhood of Swindon 

 many descriptions have been given § ; but they do not agree with each 

 other, and are all defective. Little addition has been made to our 

 knowledge of the Oxfordshire and Buckinghamshire area, although 

 Prof. Phillips in 1871 1| added the names of several and the figures 

 of a few species from the series, which he took no pains to compare 

 with those of foreign authors. The most important event in relation 

 to these rocks was the visit of M. Ssemann to this country in 1865. 

 He was struck by the resemblance of the fossils of the Hartwell 

 clay to those of parts of the Boulogne cliffs to which had been as- 

 signed the name of Middle Portlandian ; and M. De Loriol*f[, after 

 an examination of the series of fossils from this locality and from 

 Swindon, identified many as French species ; and his co-author M. 

 Pellat stated that the clay of Hartwell should be called Middle 

 Portlandian, and that the Lower Portlandian is absent from England. 

 These statements have been most useful as opening up questions of 

 the highest interest ; for it has been necessary to inquire with what 

 right the name of Portlandian has been adopted in France, and 

 whether any part of the series is absent from England, and thus to 

 reexamine some portion of the Kimmeridge Clay. 



In our introduction to the " Corallian Kocks of England "** Mr. 

 Hudleston and I regarded the series we were about to describe as a 



* Trans. Geol. Soc. 2nd ser. vol. iv. p. 17. 



t G-eol. Surv. Horizontal Sections, Sheet 56. \ Geology of Weymouth. 



§ Godwin- Austen, Q. J. G. S. vol. vi. p. 454, Mem. Geol. Survey, Sheet 34; 

 Proe. Geol. Assoc, vol. iv. p. 543. 



II Geology of Oxford and the Valley of the Thames. See also Wright, 

 * British Fossil Echinodcrms,' and Lycett ' The Fossil Trigoniae,' Pal. Sec. 



% Me moires de la Soc. Phys. et Hist. Nat. de Geneve, tome xix. 



** Quart. Journ. Geol. Soc. vol. xxxiii. p. 261. 



